Blast furnace control system



Nov- 26, 1957 o. J. LEONE BLAST FURNACE CONTROL SYSTEM 4 Sheets-Sheet 1 Filed Jan. 12. 1953 INVENTOR @jOTTO J. LEONE f Nov. 26, 1957 o. J. LEONE BLAST FURNACE CONTROL SYSTEM 4 Sheets-Sheet 2 Filed Jan. 12. 1953 INVENI'OR LEON E )OTTO J 2% Nov. 26, 1957 o. J. LEONE BLAST FURNACE CONTROL SYSTEM 4 Sheets-Sheet 3 Filed Jan. 12, 1953 INVENTOR J. LEONE OTTO Nov. 26, 1957 o. J. LEONE 2,814,479

BLAST FURNACE CONTROL SYSTEM Filed Jan. 12. 1953 4 Sheets-Sheet 4 INVENTOR OTTO J. LEONE United States Patent 2,814,479 BLAST FURNACE CONTROL SYSTEM Otto J. Leone, West Newton, Pa. Application January 12, 1953, Serial No. 330,753 18 Claims. (Cl. 266-30) This invention relates to a novel control and detection system for slips and rolls, whether incipient or otherwise, of blast furnaces. Further, this invention pertains to new, quickly responsive control apparatus combinations useful in so controlling blast furnaces.

Blast furnaces are highly individual in their operation and that operation is affected by numerous factors: Among those factors are the nature of the stock charge and its introduction into the furnace; the volume rate, temperature and pressure of the blast air fed to the furnace; the maximum permissible top pressure in the main leading from the furnace; the voids and buoyancy conditions of the downwardly moving stock; the upward gas velocities in the furnace; the presence of a common gas main from a plurality of furnaces or other associated equipment; interruptions due to the casting or to temporary down periods; the kind and response of control instruments that may be used; and human error. Whenever orderly downward movement of a charge of stock in the blast furnace shaft is interrupted by incipient formation of a bridge or a scaffold at some level in that shaft, a tendency for the furnace to hang begins. If continued, the stock below that level may continue to move, forming a cavity therebcneath, and the furnace may be said to be hanging. if the weight of the hanging materials becomes too great for the upwardly moving gases to support, the hanging material falls or slips into the cavity below with a violent disturbance of the furnace operation. The phenomenon of rolling which may appear without a stoppage of downward movement of charging stock but in which the rate of downward movement of the stock at lower levels appears to be faster than it is at upper levels, Would seem akin to hanging and slipping. With such a slip or roll there is a sudden increase in the top pressure of the furnace to a value substantially higher than normal. Such top gas pressure may increase so much that it may cause damage to the furnace equipment and endanger the furnace operators, particularly if bieeder valves, whether power or manually operated, open too late, which they may when there is a severe slip in the furnace. Even when a gas main bleeder valve does operate in time to prevent the top gas pressure from reaching and excessively high value, its opening ejects dust and gases into the atmosphere, which not only represents a loss of furnace production but also constitutes a serious air pollution problem. Such fine solids which in slips or rolls may be caught by a dust catcher usually require sintering and briquetting before that dust can be returned to the furnace.

In addition, such hanging, slips and rolls may create disruption and rearrangement of the solids burden in the furnace shaft and bring about, in severe cases, further troubles in the operation of the furnace and/or a change in the analysis of the hot metal produced.

Reference is made to the differential pressure control principles and system for avoiding hanging and slips in blast furnaces disclosed in my copending application Serial No. 749,238 for United States Letters Patent, filed May 20, 1947, now patent No. 2,625,386.

I have discovered that, particularly in the case of low pressure blast furnaces with limited permissible top pressures, a mode effective and flexible control is provided by plural regulation of both the top gas pressure in the gas main and of the pressure of the blast air supplied to the bottom of the furnace shaft through the bustle pipe and tuycres. Thereby, I can automatically control a blast furnace over a relatively wide range of conditions and variables existing therein without losing the power to maintain the stock in buoyant condition in the furnace so that it moves downwardly with good contact with the blast air supplied and without hanging or packing or building up pressure differentials across any levels in the furnace shaft exceeding those above which hanging, channeling, slipping, or rolling may result.

Further, I have discovered that the rate of increase of top gas pressure as a blast furnace builds toward and/or is in a slip or roll is greater than the rates of change of those pressures that occur in its normal operation, even through a particular furnace may normally have wide swings in its top gas main pressures. A number of new control apparatus combinations are provided herein which include floating members to quickly detect slips and rolls, whether incipient or occurring, and transmit corrective action signals to prevent or arrest such slips and rolls. The consequence is that blast furnaces may be operated for the production of hot metal therein to an extent heretofore unknown without troubles which have always been considered inherent in such operations. Moreover, even in the case of blast furnaces not practicing my differential pressure control, my new rate control principles and control apparatus combinations may be employed by such blast furnaces to quickly restore normal operation after a slip or roll, or a portion thereof, has occurred. Heretofore, after a slip or roll, such an uncontrolled blast furnace might remain in an upset condition for a cousid erable period, during which the normal production of hot metal therefrom was impeded.

Other objects and advantages will be apparent from the following description and from the drawings, which are schematic only, in which Figure l is one illustrative embodiment of a blast fur nace assembly employing various principles of this invention;

Figure 2 is a schematic view of a new pressure controller having a floating member and overtaking rate provisions to detect slips and rolls;

Figure 3 is a schematic view of a new pressure con troller which may be used to measure pressure change rates directly and provide a control signal for excessive rates of pressure change;

Figure 4 is a still further embodiment, in schematic form, of a new controller for measuring pressure change rates and initiating control signals for excessive rate changes;

Figure 5 is a schematic view of still another modifica tion of a new pressure controller measuring change rates and capable of providing a plurality of control signals in the event of excessive pressure changes of varying magnitudes;

Figure 6 is a still further embodiment, in schematic form, of a new pressure controller measuring static pressure and providing a floating member for rapid excessive rate response; and

Figure 7 is a schematic view of a new top gas pressure controller in combination with an auxiliary differential pressure controller for highly sensitive pressure change rate detection and response.

Referring to Figure 1 of the drawings, a blast furnace 10 may comprise a hearth 11, a bosh 12, a furnace stack 13 and a top 14. The hollow interior of the furnace It) comprises a furnace shaft 15. Air for the blast furnace may be drawn in through an intake housing 16 and a conduit 17 to which a blast air volume meter and controller 18 is connected by piping 19 in the usual manner.

A blower is turned by a suitable prime mover and may be regulated as to its volumetric output rate, usually in cubic feet per minute, by a regulator 22 responsive to controller 18 to which it is connected by an impulse line 23. The term impulse line" herein shall mean the piping used for conducting pressure impulses transmitted by gas or liquid through such piping and/or shall also mean electrical conduits where an electrical impulse is transmitted, whether such impulse lines lead to or away from the controller in question. The term controller" herein shall include measuring instruments disclosed herein that receive signal impulses such as the existing pressure conditions in the blast furnace assembly and yield a corrective control signal impulse, whether of the indicating, recording or other kind of measuring means.

The outlet of blower 20 is connected to a blast air pipe 21 leading into the stoves 24 for heating the blast air before introducing it through a pipe 25 into the bustle pipe 26 from which branch pipes 27 lead the hot blast or blast wind to the interior of hearth 11 through tuyeres. A by-pass pipe 28 is respectively connected to blast pipes 21 and 25 around the stoves 24 to divert some cold blast air from the stoves 24. A valve 29 linked to a valve operator 30 is usually automatically operated to divert such portion of the cold blast air from pipe 21 as will be required to maintain a generally constant hot blast air temperature at the entrance to the tuyeres near the hearth 11. A pipe 31 leads from the interior of pipe 21 to atmosphere and, with a valve 32 operatively mounted therein, constitutes the principal power-operated blast air pressure relief, or snort," valve. Usually each blast air pipe 21 is also provided with a manual snort valve 62 having a manually operated valve 63 therein for conventional snorting purposes. However, manual snort valves like valve 63 are insensitive and give rise to a great deal of trouble and the possibility that control of the furnace may be lost, particularly when the furnace is acting up so that if too much air is bled off or cut back by a furnace operator through pipe 62, the furnace may pack and remain upset for a much longer period than otherwise would be the case. A pipe 33 with a valve 34 therein, connected to pipe 31 inwardly of valve 32. constitutes an auxiliary power-operated snort valve which may be used for modulation. The term modulation herein shall mean providing incremental controlling and/ or corrective action generally along with the changes in the conditions in the functioning of blast furnace 10 which require controlling and/or corrective action. Modulation as so used is to be distinguished from onoff" controlling as will be understood by those in the field of industrial instrumentation where corrective action is reserved until an extended adverse range has been traversed in the conditions being controlled.

In top 14 of blast furnace 10, a small bell 35 and a large bell 36 are suitably mounted for the periodic in troduction of a stock charge through hopper 37 to constitute the burden of furnace 10 in shaft 15. The operation of large bell 36 is performed by means of its stem 38 and such operation alternates with the operation of bell 35. A gas main 39 communicates with the upper part of furnace shaft 15 above the stock level line for the conducting away of the gaseous products of the furnace reaction. Gas being conducted through main 39 away from furnace 10 will usually be caused to pass through a dust catcher 40 to remove stock charge dust entrained in the efiluent reaction gases and through a gas washer 41 to provide a relatively clean top gas which then may pass as clean blast furnace gas to stoves such as stoves 24 to heat them or to boilers as a fuel. A bleeder pipe 42 is usually positioned adjacent the top of a blast furnace such as blast furnace 10 communicating with the interior of main 39 to relieve excessive top pressures which may be generated in a blast furnace before such pressures blow the seals of the dust catcher or gas washer, or prevent further charging of stock, or

otherwise tend to adversely affect or to damage the equip ment and possibly endanger the furnace operators. Pipe 42 may form a seat for a gas bleeder valve 43 which may be held in normally closed position by weights 44 on a beam 45 pivotally connected to valve 43 and to a bracket 46 attached to the furnace structure. In gen" eral, it may be noted that bleeder valve 43, whether power-operated or not, is not a valve which is opened too quickly with the result that in some cases dangerously high top gas pressures in blast furnace 10 may be achieved before valve 43 opens. Even when it does open, dust, representing a loss from the furnace burden. and gases go out into the atmosphere. In many communities, the presence of such dust in the air is regarded as a serious air pollution problem. Even such dust as passes into dust catcher 40 when the bleeder valve 43 operates generally requires sintering and briquetting before it may be returned to the furnace shaft 15.

In the embodiment illustrated in Figure l, a relief standpipe 47 may also communicate with the interior of main 39 in the portion 48 thereof following washer 41. The upper end of pipe 47 opens into the atmosphere and if gas is discharged therefrom, it is relatively clean gas. A valve 49 linked to an operator 50 controls outward passage through the standpipe 47. If desired, standpipe 47 may be opened and used in lieu of bleeder valve 43 where possible to keep less dust from escaping to the atmosphere.

The embodiment illustrated in Figure l is preferably equipped to utilize my differential pressure control across the furnace 10, or any part thereof, as an indication of and for the purpose of controlling hanging and slips, .including rolls. Thus, a differential pressure controller may have the opposite sides of the manometer or other differential pressure responsive element therein connected by impulse lines 56 and 57 to a bottom pressure tap 58 and to a top pressure tap 59 respectively. The lines 56 and 57 are respectively high pressure and low pressure lines filled With air and gas for impressing upon controller 55 the current pressure differential existing across furnace 10, that is, in the illustrated embodiment. the difference between the blast wind pressure in pipe 25 and the top gas pressure in main 39. Inasmuch as hanging can occur in a furnace at the bottom, at the top and/or at intermediate levels, the taps 58 and 59 may instead be located so as to span the distance between any desired levels within the interior of shaft 15. Controller 55 may be made more sensitive and responsive to the differential pressures impressed thereon by using a compressed air relay therein connected to an external fixed air pressure source through a pipe 77 which is a continuation of supply line 76.

A novel top gas pressure controller 60 may also be connected by impulse line 61 to top pressure tap 59. Top pressure controller 60 may be electrically connected by wires 64 and 65 through a relay 54 and wires 66 and 67 to a 3-way solenoid valve 68 to admit compressed air into or to exhaust compressed air from a pressure chamber 69 through a pipe 70'. Chamber 69 is in a fast-acting operator 70 to fully open or close valve 32 and is provided with a diaphragm 71 normally pressing chamber 69 to its smallest dimensions under the influence of a spring 72. Linkage 73 connected to diaphragm 71 controls the turning of valve 32 in pipe 31. Solenoid valve 68 is provided with an exhaust port 74 and receives its compressed air through an inlet port 75 connected to a pipe 76 through which compressed air is received from some suitable supply. Normally the solenoid valve is deenergized and chamber 69 is connected to exhaust through port 74 causing valve 32 to close pipe 31.

Valve operator 78 for valve 34 is similar to valve operator 70 but is subject to modulating corrective action hereunder by the use of a valve positioner 79 having an arm 80 connected to the linkage 81 which operates valve 34. Modulating positioner 79 is connected to the upper pressure chamber of operator 78 by a variable impulse line 82 which is correlated to the action of controller 55 through impulse line 84 connected thereto. A compressed air pipe 83 connects positioner 79 to energy source 76. Modulating operator 85 for a top gas pressure valve 86, which is after (in the embodiment shown) gas washer 41 and standpipe 47, is also at the same time responsive to the control signal action of controller 55 through an impulse line 87 which joins impulse line 84. A pipe 83' connects operator 85 to the fixed pressure energy source 76. In some cases, it is possible, where the speed of the blower 20 can be reduced in modulating fashion by some percentage, to avoid the diversion of cold blast air to atmosphere through pipe 33 and save cost in the course of a differential pressure control action, by combining such blower modulation with the modulation of valve 86. A relay 89 may receive its variable control signal impulse through an impulse line 88 and be connected to regulator 22 by a further impulse line for such an alternative plural control action, in which event the valve in line 88 will be opened and the one in line 84 closed. Again, in lieu of the use of valve 34 or of relay 89, a valve 135 on the discharge side of blower 20 may be linked to an operator 136 which may receive control signals from a controller like differential pressure controller 55 to modulate the pressure of the blast wind by setting up a changed orifice in pipe 21 rather than by varying the actual mass rate of blast air supplied by blower 20. Although the impulse lines from differential pressure controller 55 are pneumatic, it will be evident electrical, pneumatic or hydraulic impulses or combinations thereof may be utilized as control signals with corresponding changes in the instrumen tation and equipment employed.

I have discovered in applying the principles disclosed in my aforesaid application, that with some blast furnace operations, more especially those with a relatively low maximum permissible top pressure and those of relatively smaller capacity or with relatively inexperienced operators, a highly flexible and greater control effectiveness with relatively more economy in operating costs and less possibility of loss of control, may be obtained by plural corrective action in generally simultaneous or substantially overlapping fashion of the top gas pressure regulating means and of the bottom or blast air pressure regulating means. Still further, I have discovered that the rate at which the top gas pressure rises in a blast furnace constitutes an indication that hanging and slipping may be incipient or under way. Thereby, a new principle is also provided by the use of which blast furnaces, whether or not they employ my pressure differential control, may be guarded against the occurrence of slips and rolls. The following description of the new top pressure controller 60 will preface a description of an operation of the Figure 1 embodiment which will bring out new features in the improvements I have disclosed herein.

Figure 2 is a schematic illustration of essential parts of top pressure controller 60 which, in its commercial form, will be encased in an instrument case 90 for mounting at any suitable control location. Impulse line 61 is provided with branches 91 and 92 in which resistances 93 and 94 are respectively incorporated. Inasmuch as impulse lines 91 and 92 are gas pressure pipes, the resistances 93 and 94 may take the form of valve orifices which may be adjusted to vary the relative resistance in the two branches 91 and 92. Branch 91 may terminate in a sealed bellows housing 95 fastened to the back of instrument case 90 and having a pressure chamber 95'. Housing 95 may be provided with a resilient bellows 96 in sealed relation to opening 97 through which a rod 98 extends. Rod 98 is rigidly connected at one end to head 99 of bellows 96 and is pivotally connected at the other end to a rate arm 99 pivoted about pin 100 which is also fastened to case 90. A pen 101 at the lower end of arm 99 may be used to mark a recording chart passed there under by any suitable clockwork mechanism, for example, which need not be illustrated. Branch 92 in turn communicates with another bellows housing 102 fastened to case and containing therein a bellows 103 which seals the interior 104 of housing 102. A rod 105 connected to head 106 of bellows 103 passes through an opening 107 for pivotal connection at 108 to a pressure arm 1.09 pivoted about the same axis pin 100. End 110 of pressure arm 109 constitutes a pointer pen to record on the aforesaid chart and to indicate top gas pressure, as in inches of water, on a scale 111 adjacent a trace of an are likely to be described by pen 110. If resistances 93 and 94 are appropriately selected with the former greater in relation to resistance 94 in this embodiment, as the top gas pressure in main 39 rises, pressure arm 109 and rate arm 99 will move in a clockwise direction about pivot 100, and depending upon the rate of the top gas pressure change in an increasing direction, arm 109 will tend to overtake arm 99. That is, if the rate of increase in the top gas pressure in main 39 and hence in impulse line 6! is great enough, such overtaking will take place and will close contacts 112 and 113 respectively mounted on arms 99 and 109. Insulating brackets 114 and 115 respectively support such contacts on their arms. An arcuately slotted guide 116 cooperates with a machine screw 117 engaging a drilled and tapped opening in finger 118 to which contact 112 is attached so that by loosening screw 117, finger 118 and thereby contact 112 can be swung about pivot 119 to shift it to a new position wherein it can be held by retightening screw 117 against guide 116. Any such repositioning enables floating contact 112 to be adjusted to arm 99 and contact 113 which is fixed, in the embodiment shown, on bracket 115.

Such relative adjustment of the contacts plus proper selection of the respective total resistances in branches 91 and 92 enable controller 60 to be set for closure engagement of contacts 112 and 113 upon the occurrence of an increase in the rate of change of the top gas pressure increases which indicates incipient slipping conditions. The new structure of controller 60 is a further provision which enables the rate arm 99 to float under relatively unvarying pressure conditions a prescribed angular distance from pressure arm 109 irrespective of the position of pressure arm 109 along its pressure-meets uring scale, until a rate of change of the top gas pressure occurs which is sufficiently high to indicate the potentiality or presence of slipping or rolling conditions. Moreover, where as in the case of human error, or loss of pressure differential control during casting, or reduction of blast air volume for a sufiicient time, a slip has actually occurred, contact 112 will be overtaken by contact 113 to bring into play that much more quickly the corrective action exerted by controller 60. Lead wires 120 and 121 from the respective contacts through terminal posts 122 and wires 64 and 65 energize. extremely quickly, the valve operator 70 to open inlet port 75 to pipe 70' closing off exhaust port 74 and depressing diaphragm 71 to open valve 32, quickly dropping the cold blast air pressure enough to supplement or override as required the continuously acting differential pressure modulating controlling exercised through controller 55 via top gas pressure valve 86 and, for example, bottom air pressure valve 34. Hence, if a slip has not occurred, there will usually be no engagement between contacts 112 and 113, whereas on the other hand. if incipient slip or slip or roll conditions have occurred, the overtaking rate principle embodied in controller 60 will quickly restore normal operations in the blast furnace to the modulating control of differential pressure controller 55.

In operation, the embodiment illustrated in Figures 1 and 2 is so constructed and arranged that the dilferential pressure controller 55 by impulses through the lines 84 and 87 will modulate the top gas pressure in main 39 including portion 48 by action of valve 86 and correspondingly modulate, in inverse manner, the blast air rate and consequently the blast air pressure by movement, for example, of auxiliary power-operated snort valve 34. For example, if furnace 10 tends to stiffen as indicated by an increase in the pressure differential across taps 58 and 59, controller 55 will move valve 86 in a closing direction in accordance with the increase in the pressure differential. Substantially simultaneously therewith, since an increase in the top gas pressure in main 39 tends to produce at least an immediate increase in the pressure of the blast air fed to the furnace, valve 34 is inversely moved in an opening direction to an extent that insures with the top gas pressure increase a flexible control of the rising pressure differential to arrest it before it reaches a value indicating the presence of bridging or scaffolding material in shaft constituting a hanging situation, or the presence of gaseous lifting velocities of an order passing upwardly through shaft 15 which promote such hanging and/or the early stages of rolling, thereby keeping the pressure differential within that range which will maintain an orderly stock movement in shaft 15 under buoyant" descending conditions. By means of such plural regulation at the top and bot tom of the furnace or by means of such regulation in materially chronologically overlapping relation, over-all control effectiveness appears to be improved in a number of respects. In the first place, the corrective increase in top gas pressure need not be as great as would otherwise be required without coincident modulation at the bottom. Further, under the new system the rate of blast air fed into furnace 10 remains high without requiring excessive cut back in the air rate and thereby in the pressure with consequent loss of production of hot metal and a tendency, at times at least, to swing" the furnace operation in terms of variation in the pressure differential across the furnace enough to tend to be upsetting to proper functioning. Under the new plural control modulation operation also, it would appear that the average blast air pressure will be lower for the same average blast air volume rates with consequent lower costs per unit of blast ai supplied. Moreover, modulation of the top gas pressure retains it better as a working control than if it alone were increased to its maximum allowable limit and appears to require less of a cut back in the blast air rate than would otherwise be the case.

Conversely. as the pressure differential across furnace 10 cases, that is as it drops into the normal operative range, valve 34 will move toward closure position in pipe 33 while valve 86 will move in an opening direction to lower the pressure differential and keep the descending stock in orderly descending relatively buoyant relation to the ascending air and gases. If the pressure differential drops below the buoyancy range conducive to orderly downward descent of the stock charge in the furnace shaft 15, the furnace burden may pack, in which event the supplying of blast air to the furnace must be continued until enough coke is burned out to create a cavity in the vicinity of the fusion zone so that descent can begin again and the control system acquire or regain fully effective mastery of the operation. Packing generally is less likely than hanging and slipping or rolling because of the tendency in blast furnace operation to keep the blast air as high as possible to keep the hot metal production up. Therefore, under the automatic plural control system disclosed herein, the descend ing stock in the furnace shaft between the hearth and the stock level, with the variable voids constituting a variable orifice therein, can be flexibly controlled and orderly buoyant forces maintained thereon so that neither the whole burden nor any part thereof either hangs or packs.

Each blast furnace has its own individuality due to the great number of variable factors that are involved in its functioning. Nevertheless, any blast furnace can have determined thereon the maximum pressure differential that may be maintained with stable operation and orderly stock descent in the furnace shaft, either by reviewing prior furnace operation pressure records if they exist, or by operating the furnace so that slipping and rolling occur and noting the pressure differential. With that last-mentioned pressure differential in hand for the particular furnace, the upper pressure differential control setting on a controller like controller may be set at any lower pressure differential figure which will not force the blast furnace to hang and slip or roll. Similarly, a lower pressure differential setting for a controller like controller 55 may be obtained, if it cannot be calculated from existing records of prior operations of the furnace, by operating the furnace under conditions, such as too low a volume rate for the blast wind, which will cause the furnace to pack, whereupon the lower pressure differential control setting mentioned may be set at any figure above that which may be so induced.

My discovery that the rate of top pressure change across a blast furnace in an increasing direction is greater in the course of incipient or actual slipping or rolling conditions, and in the course of such slipping and rolling. constitutes another principle utilizable in controlling blast furnaces. That new principle is incorporated in top gas pressure controller and is combined in the embodiment of Figure l with the control action of differential pressure controller 55. Thereby, if despite the modulation control exercised by controller 55, the furnace continues to stiffen and the build-up in the top gas pressure exceeds a rate normally to be expected, contact 113 will overtake contact 112 as described and operate the main power-operated snort valve 32 to achieve a much more rapid release of blast air and the lowering of the blast air and differential pressure. Further, that overtaking will occur in approximately the same length of time no matter where the top gas pressure is at the instant the slip build-up conditions begin. In other words, as shown in Figures 1 and 2, if the top gas pressure is at 60 inches of water in lieu of being at 15 inches of water before the accelerated rate build-up described, the angular distance between arm 109 and arm 99 will be approximately the same. However, once the slip or rolling top gas pressure build-up rate begins, arm 109 will move to overtake arm 99 and close the contacts 113 and 112. Valve operator 50 may also be connected to relay station 54 by electric lines 123 in the event that anyone may wish to open valve 49 upon the occurrence of a slip bringing contacts 112 and 113 into closure engagement. Generally, the described controlling action of valve 32 is to be preferred without recourse to valve 49.

In calibrating a controller like top gas pressure con troller 60 for a particular blast furnace, the angular distance between the arms 99 and 109 with the respective resistances and bellows operative thereon will be set so that overtaking occurs when the rate of increase in the top gas pressure exceeds some predetermined value. Generally, the bellows themselves like bellows 96 and 103 will be provided with the same range calibration to make it simpler to use in the differential mode described. Such bellows or other diaphragm elements are preferred in giving fast, low inertia response to pressure changes. That predetermined value in turn may readily be ascertained by preliminary operation of a furnace in a stable manner and noting the pressure swings of arm 109 so that the adjustment and operation of arm 99 relative thereto may be made so that the contacts 112 and 113 do not engage in the course of such normal swings. Thereby, an abnormal rate change, indicating slip or rolling buildup or occurrence, will cause overtaking and contact and constitute an appropriate calibration of controller 60. In that connection, the bell closing operations of certain blast furnaces afiect the top gas pressure. Thus, there is a rise in the top gas pressure in main 39 upon the closing of large bell 36. If desired, a switch 51 connected to stem 38 by a switch arm 52 and electrically connected to relay station 54 by electric wires 53 may be used upon the operation of bell 36 to make controller 60 insensitive to the pressure existing at tap 59 when bell 36 is moving.

In some cases, as shown in Figure 2, a top gas pressure controller like controller 60 may be provided with a maximum top gas pressure limit switch. Such a switch may have a movable contact 125 mounted on bracket 114 and a fixed contact 126 mounted on a bracket 127 fixed to the back of an instrument case like case 90. Contact 126 may have the rearward part thereof threaded and made to be turned by a thumbpiece 128. The threaded portion of contact 126 may be engaged by a nut 129 on bracket 127 so that the fixed position of contact 126 can be adjusted for the particular blast furnace with which the controller is to be used. Extensible electric wire leads 130 and 131 are in electrical contact with a pair of wires 132 and 133 which may be connected to operator 50 in the Figure 1 embodiment to operate the relief valve 49 as a safety measure it valve 32 has also been opened by the engagement of contacts 112 and 113. On the other hand, a parallel connection from wires 132 and 133 may be made to operator 70 of valve 32 so that upon the engagement of contacts 125 and 126 without engagement between contacts 112 and 113, both snort valve 32 and top pressure relief valve 49 may be opened. An outside electric power supply may be conducted to the electrical wiring shown in Figure 1 through the pair of wires 134.

It may be noted that even if a blast furnace is oper ating without any differential pressure controller like controller 55, the utilization of a top gas pressure controller like controller 60 has great utility because with a slip or rolling rate of increase in the top gas pressure being higher than rates of top gas pressure increases in the course of normal or stable operation, such blast furnaces instantly respond in a corrective manner if a floating contact like contact 112 and an overtaking pressure contact like contact 113 upon engagement are caused to instantly operate, for example, a power-operated snort valve like valve 32 to relieve the distress of the furnace and drop the tendency of the top gas pressure to reach such excessive proportions that it may open a relief valve like valve 43 or cause actuation of valve 49.

The new overtaking rate principle disclosed herein is incorporated in various other new control apparatus combinations schematically illustrated in Figures 3, 4, and 5. The parts therein generally corresponding in construction and functioning to parts in the new controller shown in Figure 2, have the same reference numerals applied thereto with the addition of the letter a" in the case of the Figure 3 structure, of the letter "b in the Figure 4 structure, and of the letter c in the Figure structure.

In Figure 3, under a steady top pressure exerted through impulse line 61a, arm 139, which is not a pressure-measuring arm but one which measures a rate of change of pressure, remains at the zero mark on an arbitrary scale 140, assuming bellows 96a and 103a have the same range calibration. If, however, the top gas pressure rises, arm 139 will swing around pivot 100a in a clockwise direction. Conversely, when that pressure falls, arm 139 will swing around in a counterclockwise direction. In the case of a rate of change portending an incipient or actual slip, that rate of change will be high enough to make contact between contact 113a and a fixed contact 141. Contact 141 is connected to a preset arm 142 connected to the back of instrument panel 900 by a slotted bracket 143 and machine screw 144. The preset position of contact 141 will be set far enough away from the zero position on scale 140 to require for engagement an increase in the rate of increase of the top gas pressure exceeding the normal rates of increase in the top gas pressure of the blast furnace to which controller 60a is applied. When contacts 113a and 141 engage, electrical impulse lines 145 energize solenoid valves 146 and 147 so that the exhausting of chamber 104a proceeds very slowly through line 148 instead of branch 92a as arm 39 is returned in a counterclockwise direction toward its zero position as the top gas pressure falls. At the same time, the retraction of bellows 96a will proceed correspondingly slowly by virtue of the reduced opening to chamber 'a through line 149 when the energization of solenoid 147 shuts off branch 91a. Such slow return acts in the manner of a time delay with respect to corrective action signals transmitted, for example, through the lines 123a and 124a which may be connected in the manner described in connection with lines 64 and 65. Conversely, if there is a decrease in the normal rate of decrease of the top gas pressure, arm 139 will move in a counterclockwise direction to the right of the zero mark on scale giving a visual indication and recording in whatever rate units the scale is marked in for that decrease. An adjustable stop 150 fastened to case 90a may be employed to limit the counterclockwise rotation of arm 139 or to act as a contact for corrective action in the event of an excessive decrease in the rate of decrease of the top gas pressure. A tank capacitance 137 and valve 138 may be used in conjunction with each bellows assembly for response flexibility and wider range of adjustment. Such flexibility is great enough to provide a means for an extensive range in presetting the factors for operation of the new rate principle set forth herein.

In Figure 4, the new rate principle may be practiced by means of a single bellows housing 10212 having therein a bellows 1031) and having opposite sides of the bellows subjected to the differential pressures exerted respectively through the branches 91b and 92b with the aid of suitably adjusted resistances 93b and 941;. Head 10Gb may be pivotally connected to a rigid link 105b the other end of which is pivoted to a crank 151. Crank 151 is rigidly secured to shaft 152 journaled in housing 102b, Shaft 152 extends through housing 1112b and pressuretight stufling glands so that chamber 1114b remains pressure tight. Arm 13% is attached to journal 152 outside of housing 1112b. A rate arm 139]; is provided with contacts 113b and 153. Contacts 111% and 153 are adapted to respectively engage adjustably preset or fixed contacts 11% and 154. Thereby, as in the case of the embodiment of Figure 3, an increase in the rate of increase of the top gas pressure, for example, beyond that which is normal, will bring contacts 112 and 11311 into engagement for corrective action such as that described in connection with the embodiment in Figure 2. The movement of contact arm 139E; past the zero position on scale 14% toward contact 154 is not significant insofar as it may indicate a decrease in the rate of decrease in the top gas pressure. However, contact 154 can be adjusted very close to the zero position of contact 153 so that if a seal-in relay (not illustrated) circuit is included and energized by engagement between contacts 112b and 113b, the effect of that engagement can be retained until said seal-in relay circuit is de-energized by engagement between the contacts 153 and 154.

Although the various contacts which have been described, other than those in connection with the new device in Figure 3 when gas may be trapped in the housings 95a and 102a by virtue of the operation of solenoids 146 and 1.47, are make-and-break contacts, it will be evident to those to whom this disclosure is made, that such contacts may be electrically connected to suitable seal-in switches to retain engagement between the respective contacts where needed to give time for the action of the equipment being correctively controlled until either a predetermined time has elapsed or the predetermined corrective action is sufiiciently under way. Thus, in the case of the embodiment in Figure 4, if contacts 1121) and 113b should engage midway between the first and second left-hand division after the zero mark on scale 1401) and then separate, such a seal-in or lockup electrical relay arrangement might be provided to continue the control signal initiated upon such engagement of the contacts 11% and 11% until pointer pin 11% has returned a predetermined distance toward the zero mark on scale 14%.

Figure illustrates a modification of a new controller like, for example, controller 600, in which the rate of change of the top gas pressure is measured by bucking or opposing the movements or displacements of two pressure responsive bellows 96c and 1030. Heads 99c and 106s are joined to a pointer 139a and thereby to each other to indicate increasing rates of increase and decreasing rates of decrease of top gas pressure on a rate scale 140a by a translatory movement of arm 1390, which will be proportional to the rate of change of the top gas pressure change. Arm 139s carries a contact 113s for engagement with a contact 141a pivotally mounted at 160 in case 906 of controller 600. An adjustment screw 161 bears against rocking support 162 for contact 1410 to hold contact 1410 in a fixed position relative to case 90c and to arm 1390 when at the zero position on scale 140a. A spring 163' holds support 162 against screw 161. A second contact 163 is mounted on the other side of support 162 and is in electrical engagement with contact 1416. A contact 164 is supported on a rocking support 165 pivoted to instrument case 900 at 166 and is adjustably fixed in position in the same manner as support 162, by adjusting screw 167 and spring 168. A scale 169 may be used for the purpose of indicating rates of change in pressure corresponding to the respective adjustment of the screws 161 and 167. For an increase in the rate of increase of the top gas pressure in a blast furnace to which instrument controller 60c is applied, which is normal, arm 139s will move upwardly as shown in Figure 5 but will not cause contacts 113s and 141C to engage. However, for conditions indieating an incipient slip or the actual occurrence of a slip, that increase in the rate of increase will be excessive and contacts 113c and 1410 will engage and set afoot corrective action, in this case, for example, and by way of illustration, through a solenoid valve 170, which functions in the manner of solenoid valve 68c but is connected so as to regulate an open cycle or fully on-off diaphragm operator 78c for valve 34c. Under conditions of a still greater increase than the described abnormal rate of increase in the top gas pressure, the upward thrust of arm 139a in response thereto will not only bring contacts 113C and 1410 into engagement but will also engage contacts 163 and 164 whereupon solenoid 68c will operatively connect valve operator 70c to the compressed air in line 76c and open main poweroperated snort valve 320 to increase the relief that would be afforded by opening valve 34c alone.

Figure 6 is still another embodiment schematically illustrating a controller which may be used, for example, as a top gas pressure controller, in place of controller 60. Parts of the new device shown in Figure 6 corresponding generally in construction and function to parts of controller 60 are given the same reference numerals with the addition thereto of the letter d. Thus, a reversible motor gear reducer set 171 may be utilized to cause an arm 172 to rock, for example, between positions A and B, thereby rocking a plate 173 about the pivot 100d. Plate 173 is provided with pivotal contacts 174 and 175 pivotally connected to plate 173 and held in preset position against stops 176 by springs 177. Floating arm 99d is connected to plate 173 by a screw clamp 178 passing through arm 9% and an arcuate slot 179. Hence, the oscillation of motor 171 rocks plate 173 and arm 99d to 9. corresponding extent. The contacts 174 and 175 act as follow-up switches in conjunction with the common contact 180 on both sides of the upper end of pressure arm 109d above pivot d. A clockwise movement of pressure arm 109d occurs upon an increase in the top gas pressure exerted through impulse line 61d and switch 180175 will tend to maintain the arm 99d in floating relation to arm 109d, regardless of the angular position of arm 109d about pivot 100d. For example, if there is a normal increase in the top gas pressure and right-hand contact 180 engages contact 175, motor 171 will be energized to move arm 172 clockwise toward its limit position B through the respective electrical connections that are illustrated as leads 181 and 182 and wires 183 and 184. Such engagement of contacts 180 and tends to move the upper part of arm 109d into central position between the contacts 174 and 175 and maintain contact 112d floating relative to contact 113d. On the other hand, under the new rate principle disclosed herein, an incipient slip or roll or an actual slip or roll will send the rate of increase in the top gas pressure so high that arm 109d will overtake arm 99d, closing contacts 112d and 113d because of the relatively slower oscillating movement of motor 171. Engagement between contacts 112:! and 113a will energize solenoid 68d, for example, in the manner described earlier. In the new structure of Figure 6, a conventional time-delay device 185 may also be incorporated so that upon the engagement of contacts 112a and 113d, even though that contact is momentary, timer 185 will produce such delay as may be necessary in the time that the solenoid in valve 68d must remain energized to effect corrective action. Such timed delay or other holding as by seal-in relays may be applied to the other momentary types of contacts set forth herein where it is desirable to incorporate such a duration factor in the operation of the new system and apparatus or parts thereof. In the event of a decrease in the top gas pressure which causes bellows 1030 to move to the right in housing 102d, arm 109d will swing in a counterclockwise direction engaging left-hand contact and contact 174 to energize motor 171 through leads 182 and 186 and wires 184 and 187 to swing arm 172 in a counterclockwise direction toward its limit position A to maintain the general floating character of contact 112d relative to contact l13d until overtaken by that contact.

Figure 7 shows a mode of control of the opening of the air blast pressure relief valve that utilizes the combined measurement of the top gas pressure and of the differential pressure through the furnace in such manner that (assuming the big bell limit switch circuit 28-2 to be open. and the high pressure contacts 203 and 204 of the top pressure instrument 249 to be open) a closing of the contact 201 on the pressure arm 200 with the high rate contact 202 will not energize the 3-way solenoid valve coil 284 to operate the valve 283 to open, unless during the time that the circuit between contacts 201 and 202 is closed during an increase in top pressure, contact has also been made in the dilTerential pressure control instrument 248 between the contact 226 on the arm 224 and the low rate contact 228 by a decrease in differential pressure, and further the coil 284 cannot become energized to open valve 283 unless the closure between the contacts 201 and 202 has occurred at precisely the same time or before the contacts 226 and 228 have closed. The advantage of this arrangement is that the distance between contacts 201 and 202 in instrnument 249 may be set much closer than otherwise. The distance between contacts 226 and 228 in the differential pressure controller 248 would be set far enough apart that 226 and 228 would contact each other to close this part of the circuit only at magnitudes in the movement of the pointer arm 224 that result from slips. Preferably the instruments 248 and 249 are selected for almost equal sensitivity, if the same pressure change were impressed in the respective pressure lines 217 and 244, and with equal settings of the restrictions 216 and 214 and of the restrictions 241 and 243. These restric- 13 tive needle valves may then be set so that the pressure arm 200 (of 249) on an increasing top pressure will move faster than will the diiferenti=-.l pressure arm 224 (of 248) for the same rate of change of pressure.

Referring to Figure 249 is the top gas pressure controller, of which 210 and 210a are pressure responsive bellows connected to a common top gas pressure line 217, by means of branch pressure tubes 215 and 213. Each of the pressure tubes contains a restrictive or needle valve, 216 and 214 respectively, which are manually adjustable to provide any desired value of resistance to the flow of gas as the impressed gas pressure changes. By means of a link 212 changes in length of the pressure bellows 210a are transmitted to a high rate contact arm 208 at a pivot connection 212a, the movement of link 212 causing arm 208 to rotate about a fixed shaft 207. Similarly, bellows 210 causes a pressure-measuring arm 200 to rotate about the fixed shaft 207 in response to gas pressure changes in line 217, by means of the motion link 211 which is pivoted to pressure-measuring arm 200 by a pin 211a. A calibrated scale 206 may be provided to indicate the value of the top gas pressure.

An electrical contact 201 mounted on an insulated base is attached to arm 200 and moves with it. Similarly, a high rate contact 202 is attached adjustably by a slot 219 to an insulated base 209 which is attached to the high rate arm 208. Flexible leads 220 and 221 connect the contacts 202 and 201 to terminal connecting screws on a terminal block 218 which is of insulating material.

Referring further to the top pressure instrument 249, the insulating block 209 may also carry a second high contact 203 which also moves as the high rate arm 208 is moved by pressure changes. Cooperating with the contact 203 is a fixed-position contact 204 which may be manually set in bracket 205 so that the contacts 203 and 204 will close an electrical circuit if the pressure arm 200 reaches some high predetermined pressure value on the scale 206. The contact mechanism 204 is mounted on an insulated block support. When contacts 203 and 204 close the circuit 292 is also closed, to energize apply air pressure to valve operator relief valve 283.

The differential pressure controller 248 is built similar to the top pressure controller 249, except that it is equipped with a low rate contact 228 that moves with contact arm 236 instead of a high rate contact and arm as in the case of instrument 249. The difference in operation between 249 and 248 then is such that, whereas contacts 201 and 202 are closed by an increase in the common pressure supply at 217, the contacts 226 and 228 are closed by a decrease in the pressure supplied at 244.

The bellows 237 and 233 may be similar to 210 and 210a or they may be of different ranges; this in itself does not matter much provided the response rate of instrument 248 is adjusted to make it faster or slower than that of instrument 249, but preferably slightly slower. This can easily be done by watching the movements of pointers 224 and 200, during a slip in the furnace, for example, and adjusting the restrictive needle valves 216, 214, 241, and 243, as well as any other resistances in the pressure system, such as any valves in lines 217 or 244, until arm 224 moves slower than arm 200 during a slip. A calibrated scale 225 may be used, or the markings may be arbitrary as it is not necessary to know the true differential measure, but only to be able to set the distance between contacts 226 and 228 so that they will close during a slip.

In practical operation of blast furnaces the differential pressures are usually as much as 10 to 14 lbs. higher than the top pressure. Rather than to make the calibration of the bellows 237 and 233 in instrument 248 the same as the ranges for bellows 210 and 210a in 249, and in order to adapt the differential pressure controller 248 to commercially available differential transmitting or integrating devices such as those operating on compressed 288 which opens the the solenoid 284, and to air, and which send out output air pressure signals to the receiver that vary from 0 to 17 lbs. per sq. inch gage, for example, it may be preferable to use higher calibration ranges in 248 than in 249. With reference to top pressure instrument 249, if the top gas pressure is to be directly impressed on the instrument through pipe 217, the calibration or range characteristics of both bellows should be such that at the maximum top pressure to be indicated or recorded, the pressure arm pointer 200 will be moved from the no-pressure or zero reference position on the scale to the maximum calibration mark on the scale 206. A typical range for the top pressure controller 249, on the furnaces that are now equipped with differential control, for example, would be a range of 0 to inches of water. The bellows 233 and 237 of the differential instrument 248 would have air pressures of O to 17 lbs. per sq. inch impressed at the pressure connection 244 if used to operate from standard commercial pneumatic instrument differential transmitters.

The position of the differential pressure transmitter is shown as 256 in Fig. 7. The differential pressure measured through the furnace is connected to the measuring element of the differential transmitter 256 by means of the top pressure impulse line 250 and the blast pressure impulse line 251, in which are also located shut-off valves 254 and 253 respectively. An equalizing valve, not shown in Fig. 7, may also be used if desired. By closing the valve 254 in line 250 and opening a valve 252 to atmosphere, the calibration of instrument 256 may be easily checked by impressing known air pressures from line 251. A compressed air supply line 255 furnishes compressed air for the operation of the pneumatic transmitter 256 and to line 244.

Fig. 7 also shows electrical relays operating from coils 257, 263, 269, 275, and 295, that are connected into the electrical control circuit between the coil of solenoid valve 284 and the instrument controllers 248 and 249. These relays may be enclosed in a common relay and junction control box or housing, for example. similar to the relay or junction box designated as item 54 in Fig. 1. Power supply lines 246, 247, and 134 are shown to the instruments and to the relays and solenoid valve.

The relay equipped with coil 257 is energized when contact 226 touches contact 228 on a decrease in differential pressure as measured by the counterclockwise movement of differential pressure arm 224 in instrument 248. This relay has two sets of normally open contacts that are closed by the movement of an armature 262 when coil 257 is energized. One set of contacts is shown as 258 and 259, the other set as 260 and 261.

The relay equipped with coil 263 operates to energize the coil when contacts 201 and 202 touch each other in the top pressure instrument 249. This relay has a set of normally closed contacts 265 and 266, and a set of normally open contacts 267 and 268, which are connected to a common armature 264. When coil 263 is energized the normally closed set of contacts 265 and 266 is moved to open-circuit position, while at the same time the normally open set of contacts 267 and 268 is moved from the open to the closed-circuit position.

The relay using operating coil 269 is equipped with an armature 270 having one set of normally closed contacts 271 and 272 and one set of normally open contacts 273 and 274. This relay is so interlocked with the relays operated by coils 257 and 263 and with the solenoid relay coil 284 (and if. the normally closed contacts 277, 278, 279, and 280 of the interlocking relay coil 275 which operates from the big bell rod movement, to be described later, are closed) that the circuit through wires 293 and 294 to the solenoid valve coil 284 cannot be energized unless both sets of contacts 201 and 202 and 226 and 228 energize relay coils 263 and 257, respectively, and if coil 263 is energized at precisely the same instant or before coil 257 is energized. That is to say, in order for the coil 284 to be energized (with the aforementioned contacts 277, 278, 279, 280 closed), relay coil 263 must already be in the energized position when relay coil 257 is energized. If relay coil 257 is energized (by closing of contacts 226 and 228) before relay coil 263 is energized (by the closing of contacts 201 and 202), then it is impossible to energize solenoid coil 284 by closing the circuit through lines 293 and 294. It may be seen, therefore, that the circuit through lines 293 and 294 can only be closed if the top pressure increases at almost the same time that the differential pressure decreases, and only if the changes are great enough that there will be a period when both sets of contacts 201 and 202, and 226 and 228, respectively, will be closed. The relative time of closure of each pair of contacts does not matter; one pair may be closed for a longer or shorter time than the other, but it is necessary that for some time at least, both pairs will be simultaneously closed. The relative periods of closed circuit by the closing of each pair of contacts 201 and 202, or of 226 and 228, may be controlled to some degree by the settings that will be made by the respective restrictive needle valves 216 and 214, or 241 and 243. Alternately a timer may be used to control the time that either or both circuits are closed, in a manner similar to that shown in Fig. 6 if it is desired to control the time duration that the control circuits are closed once the contacts are made, or after the contacts are opened once they have been closed.

Figure 7 shows a means for interlocking the closing stroke of the big bell operation during charging to prevent possible accidental opening of the valve 283 by the increase in top pressure, if by some chance it may be found on some furnaces that at times the rate of top pressure increase (as the top pressure returns to normal after the closing stroke of the big bell operation to charge materials into the furnace) were fast enough to open valve 283 even though there was no slip. The limit switch 282 and the relay coil 275 are energized by electric current supplied from power source lines 246 and 247 when the contact circuit in limit switch 282 is closed. By operating a lever-operated type limit switch 282 from the movement of the large bell rod 38e, in a manner similar to that shown in Fig. l, the limit switch 282 closes its contacts to energize relay coil 275 through wire 281, which in turn moves relay armature 276 to open the normally closed contacts 277, 278, 279 and 280 in circuits 293 and 294. By setting the limit switch 282 to open the circuit in lines 293 and 294 as soon as the big bell starts to close, and by again closing the limit switch contacts when the big bell is in the closed position again, any accidental operation of valve 283 by energizing solenoid coil 284 from the closing of contacts 201 and 202, and 226 and 208, respectively, will be prevented. However, in case a slip should occur during this interval, the top pressure arm 200 must travel suflicient distance as the result of the pressure increase that it will cause the extreme high pressure contact 203 to touch the fixed position high rate contact 204, which will then close a circuit from power source lines 134:? which are also wired to operate the solenoid valve coil 284 by means of an interlocking relay whose contacts are so connected to the solenoid valve coil 284 that the coil may be energized to cause valve 283 to open independently of any control action in effect at the time in circuit lines 293 and 294, or due to energizing the relay coil 275 due to the operation of the limit switch 282. When contacts 203 and 204 close due to a high rate of increase of top pressure, as may be caused by a slip, they cause the circuits to be closed between the wires 222 and 223, and cause electric power to flow by means of the wires 291 and 292 which carry electric current from the power source l34e to the interlocking relay coil 295 having an armature 297 and its associated normally open sets of contacts 296 and 298, and 299 and 300. Connecting wires 301 and 302 convey the electric power from two sets of relay contacts to the circuit of solenoid coil 284, by connecting contact 298 through wires 302 and 303 to the wire 289 leading to one terminal of coil 284; the lead 301 connects contact 300 to provide a current flow path to the other terminal of the coil 284 by virtue of its being attached to the wire 290. Any closure of the contacts 203 with 204 will result in the coils 295 and 284 being energized and thereby causing the valve 283 to quickly bleed blast air to atmosphere. To energize the circuit shown in Figure 7, one line of an electric power source may be connected to line 247 and also to line 223, while the other line of the power source may be connected to line 246 and to line 291. While it is believed that the need for a limit switch 282 and the interlocking of the relay coil 275 and its contacts will not be necessary for any furnaces with which the differential pressure control method has been used, it is mentioned in case the need for such a provision should ever arise.

Referring to the description of the 3-way solenoid valve 284 and the relief valve operator 288, a source of air pressure may be supplied to the diaphragm of the airoperated motor 288, by energizing the valve solenoid coil 284 so that air pressure will pass through the valve body to the air motor unit by means of the connecting pipe 287. With the coil 284 of the solenoid valve in a deenergized state, the valve port into which the air pressure supply line 285 is connected is normally closed; at the same time the port 286 is opened to atmosphere; the port into which pipe 287 is connected is open whether the solenoid valve is energized or de-energized.

In connection with the differential controller 248 in Fig. 7, while it has been described as a pressure receiver connected by pressure transmitting pipe 244 to a differential pressure transmitter 256, the differential pressure transmitter may be replaced by the differential pressure controller 55 shown in Fig. 1. In that case the air supply line 255 in Fig. 7 is equivalent to pipe 77 in Fig. l; the pressure line 244 in Fig. 7 would then be connected into a controlled air pressure line equivalent to pipe 84 in Fig. 1. It is to be understood also, that while I have used the basic mechanism of Fig. 2 as the top pressure controller 249 and the differential pressure controller 248 of Fig. 7, any of the mechanisms shown in the Figs. 3, 4, 5 or 6 may be incorporated in the instruments 249 and/or 248 in place of the type of mechanisms shown in Fig. 7. And, as shown, parts 221, 209, 219, 220, 211a, 212, 212a, 207, 215, 213 and 218 in basic mechanism 249 function in the manner of parts 227, 229, 230, 231, 235, 238, 239, 239a, 240, 242 and 245 in controller 248, respectively.

As an alternate to interlocking the differential pressure measurement between pressure lines 250 and 251, as indicated by the pressures in pressure line 244, with the top pressure measurement in lines 250 and 217 in Fig. 7, I may also take the pressure for operating the instrument 248 directly from the blast line 251 only, and in this way to influence the operation of the solenoid valve 284 and valve 283 by the interconnected control action of the top pressure and of the blast pressure. For this purpose the pressure pipe 253 may be connected directly to the connecting pipe 244 of instrument 248. While this alternate method may not respond quite as fast as by interconnecting differential pressure with top pressure, it may nevertheless be used in a similar manner. Any reference to the use of interconnected control actions between the top pressure and differential pressure will therefore be understood to be substantially the same as the effect of interconnecting the control actions between the top pressure and the blast pressure.

Various embodiments and practices of this invention have been disclosed herein without limitation of the invention thereto and various other modifications may be made Without departing from the spirit of this invention or the scope of the appended claims.

I claim:

1. in a control for a blast furnace, in combination, a

pressure tap responsive to the top gas pressure in said furnace, means including a diaphragm member connected to said pressure tap and substantially solely responsive to changes in said pressure in said blast furnace, a contact movable by said diaphragm member in a particular direction in accordance with increases in said pressure, and a second contact spaced from said first mentioned contact in said direction, said spacing being sufficiently distant so that normal rates of increase in said pressure will not bring said contacts into engagement where as abnormal increases in the rate of increase of said pressure will, and means operative upon the engagement of said contacts to provide a differential of pressure across said furnace conducive to orderly downward movement of stock in said furnace.

2. In a control for a blast furance, in combination, a pressure tap responsive to the top gas pressure in said furnace, means including a diaphragm member con nected to said pressure tap and substantially solely responsive to changes in said pressure in said blast furnace, a contact movable by said diaphragm member in a particular direction in accordance with increases in said pressure, a second contact spaced from said first mentioned contact in said direction, means for maintaining said spacing generally uniform under any relatively steady value of said pressure, said means further being adapted to maintain said spacing sufliciently distant so that normal rates of changes in said pressure may change said spacing at the time being without bringing said contacts into on gagement, and means operative upon the engagement of said contacts to provide a differential of pressure across said furnace conducive to orderly downward movement of stock in said furnace.

3. In a blast furnace control system, in combination, pressure taps respectively communicating with different levels of said blast furnace, said blast furnace having a blast air supply, a pressure differential controller connected to said pressure taps, pressure regulating means including valves respectively adjacent the top and bottom of said furnace, an impulse line extending between said L controller and said pressure regulating means to transmit signals for corrective regulation of the pressure differential existing across said pressure taps by selective modulation of at least one of said valves, a top gas pressure controller responsive to an excessive increase in any rate of increase in the top gas pressure as communicated by any of said signals, valve means connected to said blast air supply to said blast furnace, and a second impulse line extending between said top gas pressure controller and said last mentioned means to open said valve means and thereby augment or hasten the corrective action of said pressure differential controller whenever said excessive increase occurs.

4. In a blast furnace control system, in combination, a pressure differential controller responsive to pressure to control the pressure difierential between the top and bottom of said furnace, a top gas pressure controller responsive to a predetermined rate of increase in the top gas pressure of said blast furnace, said last mentioned controller having a member movable in response to said predetermined rate and a member floating in closely spaced relation thereto for engagement by said first mentioned member upon the occurrence of such predetermined rate of increase, and a second differential pressure controller adapted to measure a predetermined decrease among any rates of decrease of said pressure differential and to transmit a corrective control signal to said first-mentioned pressure differential controller in the event of such engagement and the occurrence of such a predetermined decrease.

5. In a blast furnace control system, apparatus comprising, means operative to measure the differential pres sure across the blast furnace, means responsive to said differential pressure in accordance with said measurements to keep said differential pressure Within a range conducive to orderly downward movement of the furnace burden by performing at least one selective modulating action among actions for raising the top gas pressure and lowering the blas air pressure, means responsive substantially solely to any excessive rate of increase in said top gas pressure as indicative of abnormal conditions among the rates of increase in said top gas pressure, and means operative upon the occurrence of any such excessive rates of increase to reduce the blast air pressure at the time being.

6. In a blast furnace control system, apparatus comprising, means operative to indicate the differential pressure across the blast furnace, means responsive to said differential pressure in accordance with said indications to keep said differential pressure within a range conducive to orderly downward movement of the furnace burden by performing at least one selective modulating action among actions for raising the top gas pressure and lowering the blast air pressure, means responsive substantially solely to any excessive rate of increase in said top gas pressure as indicative of abnormal conditions among the rates of increase in said top gas pressure, means operative upon the occurrence of any such excessive rates of increase to reduce the blast air pressure below that existing at the time of said occurrence, and means responsive to the cessation of any such excessive rates of increase to return control to said second-named means.

7. In a plural control for a blast furnace having a blast air pipe, in combination, pressure taps respectively communicating with different levels of said blast furnace, a power-operated auxiliary snort valve connected to the blast air pipe at the bottom of said furnace, a valve in the gas main leading from the top of said blast furnace, a differential pressure controller connected to said pressure taps, an impulse line extending from said controller to transmit signals varying in accordance with the pressure differential existing across said pressure taps, means to integrate the corrective action of both said valves by the modulation thereof concurrently and in accord with said signals, and means to measure excessive rates of increase in the top gas pressure of said blast furnace and transfer corrective action control to said last mentioned means from said controller upon the occurrence of such a predetermined rate of increase in said top gas pressure.

8. In a plural control for a blast furnace, in combination, pressure taps respectively communicating with differential levels of said blast furnace, a blower to supply blast air to said furnace, means to regulate the speed of said blower, a valve in the gas main leading from the top of said blast furnace, an operator connected to said valve to modulate the same, a differential pressure controller connected to said pressure taps, an impulse line extending from said controller to transmit signals varying in accordance with the pressure differential existing across said pressure taps, said means and said operator being connected to said impulse line to generally concurrently proportion the corrective action of both said means and said valve with said signals, and a top pressure controller adapted to sense rates of increase in the top gas pressure of said blast furnace and to take over corrective control action upon the occurrence of such rates of increase in said top gas pressure beyond a predetermined rate of increase.

9. In a pressure instrument, a movable contact swingably responsive to the rate of change of a pressure, said movable contact having a zero position for a steady pressure, a second contact spaced from said zero position by a distance greater than the amplitude of the swings of said movable contact under normal operating conditions wherein such a pressure is exerted, and means for engaging said contacts when said rate of change is greater than a predetermined quantity.

10. In a pressure instrument, a movable contact responsive to a pressure, a second movable contact, means for maintaining the second movable contact in relatively uniformly spaced relation to the first mentioned contact, said means being operative at a rate less rapid than the response of said first mentioned movable contact when a change in pressure occurs, and means for causing said first-mentioned movable contact to overtake and engage said second movable contact when an excessive rate of change in pressure occurs.

11. In a pressure instrument, a pressure impulse line, a flexible diaphragm member connected to said impulse line and responsive thereto through a branch line, a second flexible diaphragm responsive to the pressure in said impulse line and connected therethrough to a second branch line, said branch lines being in parallel and having different fluid flow resistances respectively therein, the first mentioned of said diaphragm members being connected to a pressure responsive contact arm, the second of said diaphragm members being connected to a further pressure responsive contact arm to independently move said further pressure responsive contact arm, said contact arms having a common axis, and means for changing the angular relation between said respective contact arms upon the occurrence of rate changes in the pressure in said impulse line.

12. In a pressure instrument, a pressure indicating impulse line, opposed diaphragm members connected to said impulse line for operation thereby at respectively different rates, a contact arm connected to both said diaphragm members, means for moving said diaphragm members and said contact arm in accordance with a rate of change in the pressure in said impulse line, a first contact for engagement by said contact arm upon the occurrence of such change, means for delaying the return of said contact arm immediately following the end of such change, and a second contact for engagement by said contact arm when said rate of change exceeds a predetermined magnitude.

l3. ln a pressure instrument. a pressure impulse line. a bellows housing, a bellows in said housing, a branch line connected to said impulse line and to the interior of said housing exteriorly of said bellows, a second branch line connected to said impulse line and the interior of said bellows. fluid flow resistances of unlike magnitudes in said branch lines, a contact arm linked to said bellows responsive to rates of change in pressure in said impulse line. said contact arm being pivoted, and other contacts on each side of said contact arm, and means to cause at least one of said other contacts to be engaged by said contact arm upon the happening of an excessive rate of change thereby moving said contact arm a greater distance in that direction.

14. In a pressure instrument, a pressure impulse line, an axially movable bellows connected to said impulse line through a branch line, a pivoted contact arm connected to said bellows. a second flexible bellows connected to said impulse line through a parallel branch line, a second con tact arm connected to said second bellows about said pivot, said respective bellows being connected to their respective contact arms at approximately the same distance from said pivot, said respective branch lines having fluid flow resistances of different magnitude respectively therein. a third contact, one of said contact arms being operated through said branch line having a lower resistance therein and being on the outside of the other of said contact arms opposite to said third contact, and means to cause the outside contact arm to overtake and contact said other contact arm upon a change in pressure in said impulse line beyond a predetermined magnitude causing movement toward said other contact arm, and both said contact arms will move toward said third contact to cause engagement thereof upon a still further change in pressure in said impulse line beyond said predetermined magnitude.

15. In a pressure indicating instrument, a pressure impulse line, axially movable members in opposed relation, a contact arm connected to both said members,

said members being respectively connected to said impulse line by branch lines having differential resistances therein to enable said contact arm to measure rates of change of pressure in said impulse line, at least a pair of contacts in alignment with said contact arm, said pair of contacts being spaced from said contact arm and from each other whereupon a rate of change of pressure of one magnitude in said impulse line will bring said Contact arm into contact with the nearer of said pair of contacts while a greater rate of change of pressure will bring said contact arm into contact with both said pair of contacts.

16. In a pressure indicating instrument, a pivoted contact arm, a diaphragm member connected to said contact arm to move it, an impulse line connected to siid dia phragm member to move said contact arm in response to changes in pressure in said impulse line, a follower plate pivoted about the same axis as said contact. arm, movable contacts on said follower plate on each side of said contact arm, a reversible motor to oscillate said follower plate generally in accordance with the movements of said contact arm, a second contact arm attached to said follower plate in angular relation to said first mentioned con tact arm, and a contact on said last'nanied contact arm to engage said contacts on said follower plate respectively.

17. In a control for a blast furnace, in combination, pressure taps respectively communicating with different levels of said blast furnace, a power-operated snort valve connected to the blast air pipe at the bottom of said furnace, a valve in the gas main leading from the top of said furnace, a differential pressure controller con nected to said pressure taps, an impulse line extending from said controller to transmit signals varying in accordance with the pressure diflferentiul existing across said pressure taps, means to operate at least one oi said valves in response to said signals to maintain said pressure diiferential within a range conducive to orderly dmvmvard movement of stock in said furnace, and means to indicate an excessive rate of increase in the top gas pressure of said blast furnace and to operate said snort valve in response to said indication to provide a differential pressure across said furnace within said range.

18. In a pressure indicating instrument, diaphragm member movable in response to a variable pressure condition in a system, a movable contact connected to said member to indicate said pressure condition, a second mcmber generally movable at a rate different from the rat-2 of movement of said first-named member, said members being interconnected to indicate movements of said firstnamed contact at least beyond a predetermined distance for normal variations in said pressure condition, and a second contact in positioned relation to said first-named contact to enact therewith to provide a signal impulse upon the occurrence of a predetermined abnormal rate of variation. in said pressure condition when said firstnamed contact moves beyond said predetermined distance.

References Cited in the file of this patent UNITED STATES PATENTS Re. 20,092 Mason Sept. 1, 1936 2,005,773 De Florez June 25, 1935 2,031,502 Powell Feb. 18, 1936 2,041,014 Norton May 19, 1936 2,083,046 Burke June 8, 1937 2,092,560 Runaldue Sept. 7, 1937 2,228,769 Klinker Jan. 14, 1941 2,436,444 Merrick Feb. 24, 1948 2,479,616 Hasselhorn Aug. 23, 1949 2,529,875 Howard Nov. 14, 1950 2,625,386 Leone Ian. 13, 1953 2,633,858 Eckman Apr. 7, 1953 2,656,429 Tietjen Oct. 20, 1953 FOREIGN PATENTS 575,562 Germany Apr. 29, 1933 530,377 Great Britain Dec. 11, 1940 

